1. Field of the Invention
The invention relates generally to semiconductor processing systems. In particular, the present invention relates to a load lock system for coupling a high-pressure processing module to existing semiconductor processing tools that operate at or near vacuum.
2. Description of Related Art
Semiconductor fabrication typically processes substrates, such as circular wafers, into semiconductor chips by sequentially exposing each substrate to a number of individual processes, such as photo masking, etching, implantation, and cleaning. Modern semiconductor processing systems often include cluster tools that aggregate multiple processing chambers around a central transfer chamber housing a substrate handling robot. The multiple processing chambers may include, for example, degas chambers, substrate pre-conditioning chambers, cool down chambers, transfer chambers, chemical vapor deposition (CVD) chambers, physical vapor deposition chambers, etch chambers, or the like.
The various processing chambers and the transfer chamber can be isolated from one another to limit potential contamination of the semiconductors and to ensure that optimal processing conditions are maintained. Examples of cluster tools can be found in U.S. Pat. Nos. 5,955,858, 5,447,409, 5,469,035, and 6,071,055, all of which are incorporated herein by reference.
Conventional processing performed in these processing chambers, such as Low Pressure Chemical Vapor Deposition (LPCVD), typically occurs at or near vacuum. Accordingly, a load lock is typically provided to introduce a substrate at atmospheric pressure into the cluster tool kept at vacuum
Semiconductor fabrication also typically requires cleaning resist and/or etching residue from the surface of the substrate. Generally, there are two methods for cleaning the surface of a substrate, namely, wet and dry processing. Wet processing consists of a series of steps of spraying and/or immersing the substrate in expensive chemical solutions that are typically not environmentally friendly. Instead, dry processing consists of a series of steps that use gasses instead of wet chemical solutions to clean the substrate. For example, ashing using an O2 plasma.
More recently, supercritical fluids, such as carbon dioxide (CO2) with or without co-solvents or surfactants, are now being used to clean or strip photoresists or post-etch residue from semiconductor substrates. Supercritical cleaning is, therefore, a cleaning process that is neither wet nor dry.
Cleaning with supercritical fluids is desirable, as such fluids retain the properties of a liquid, but have the diffusivity and viscosity of a gas. The solvency of supercritical fluids can be enhanced by the addition of chemical agents or co-solvents that interact with materials used in semiconductor manufacturing. The supercritical fluid, with or without a co-solvent, typically acts as a solvent to remove contaminants from the wafer surface and effectively clean the surface of the substrate.
Supercritical fluid cleaning technology can be applied in many industrial processes to significantly reduce or eliminate the use of hazardous chemicals, to conserve natural resources such as water, and to accomplish tasks previously not possible, such as rapid precision cleaning of small features (e.g., resist images, VLSI (Very Large Scale Integration) topographical features such as vias, etc.) of semiconductor devices.
Moreover, cycling pressure between high and low limits near the supercritical pressure and temperature may be practiced to achieve particular process performance. This is otherwise known as phase shifting.
Accordingly, supercritical fluid processing may be safer, less expensive, and more performance effective as compared to conventional wet or dry processing. However, unlike conventional processing, supercritical technologies require high-pressure working environments to maintain the supercritical fluid phase. Also, the effectiveness as a solvent of supercritical fluids is increased with increasing pressure.
Because of the large differences in working pressures, supercritical fluid cleaning is typically kept separate from conventional semiconductor processing. Therefore, when supercritical fluid processes are required, a substrate being processed in a cluster tool must first be removed from the cluster tool before being positioned in the supercritical fluid cleaning module. Thereafter, the substrate may need to be removed from the supercritical fluid cleaning module and repositioned in the cluster tool for further processing. This drastically decreases the overall throughput afforded by current automated cluster tool technology and increases the likelihood of contamination due to such transfers.
Coupling supercritical fluid cleaning modules to existing cluster tools has numerous challenges, including the large differences in pressures between the conventional processes and the supercritical fluid processes, the cycle time needed to pressurize and de-pressurize the process chamber, and contamination of the transfer chamber by particulates removed in the supercritical fluid cleaning module. Accordingly, a method and system for coupling a supercritical fluid cleaning module to existing automated processing tools would be highly desirable.